Polyimides from 2,6-diamino-s-triazines and dianhydrides

ABSTRACT

Triazine-based polyimides are prepared by first reacting dianhydrides with s-triazine compounds containing at least two primary aromatic, aliphatic or cycloaliphatic amino groups to give triazine-based polyamic acids which, on curing, yield the polyimides. The polyamic acids are soluble in organic solvents or ammonium hydroxide, the latter yielding the aqueous solutions. From said organic or aqueous solutions useful fibers, films, adhesives, coatings and composites can be prepared. The triazinebased polyimides possess high temperature oxidative stability, good mechanical properties and electrical properties and low void contents.

United States Patent Kray et a1.

POLYIMIDES FROM 2,6-DIAMINO-S- TRIAZINES AND DIANHYDRIDES Inventors:Raymond J. Kray, Berkeley Heights, N.J.;

Roland A. E. Winter, Armonk, NY.

Assignee: Ciba-Geigy Corporation Filed: Aug. 1, 1969 Appl. No.: 889,017

US. Cl. ..260/65, 1 17/ 124 E, l 17/ 126 GR, 1l7/128.4,117/132 C,1l7/l38.8 D, ll7/138.8 E, l17/l38.8 UF, 117/145, 117/148, 117/155 R,161/197, 161/214, 161/227, 260/29.2 N, 260/30.2, 260/30.6 R, 260/30.8 R,260/30.8 DS, 260/32.2, 260/32.6 N, 260/32.8 N, 260/37 N, 260/47 CP,260/78 TF ..C08g 20/32 ..260/47 P, 65, 78 TF, 78.4, 260/249.5, 249.6

Reierencs Cited UNITED STATES PATENTS 3,179,630 4/1965 Endrey ..260/78[4 1 May 30, 1972 3,342,774 9/ 1 967 Hoegger ..260/47 3,448,080 6/1969Hirsch ....260/65 3,528,937 9/1970 Reynolds et al. ..260/29.2

Primary Examiner-William H. Short Assistant Examiner-L. L. Lee

Attorney-Karl F. Jorda, Bruce M. Collins, Martin .I. Spellman and NestorW. Shust 57 ABSTRACT 7 Claims, No Drawings POLYIMIDES FROM2,6-DIAMINO-S-TRIAHNES AND DIANHYDRIDIS DETAILED DISCLOSURE wherein R isa tetravalent radical containing at least one ring of six carbon atoms,said ring characterized by benzenoid unsaturation, the four carbonylgroups being attached directly to separate carbon atoms in a sixmembered benzenoid ring of the R radical and each pair of carbonylgroups being attached to adjacent carbon atoms in a ring of the Rradical;

R is a divalent organic radical selected from aromatic, aliphatic andcycloaliphatic series;

R is hydrogen, amino, diarylamino, di(lower)alkyl amino, anilino,N-(lower)alkyl anilino, diphenylamino, pyrrolidino, piperidino, phenylor chloro groups;

n is an integer of 5 or more.

The (lower)alkyl group employed herein means a straight, or branchedchain alkyl group having up to four carbon atoms. Examples of suchgroups are methyl, ethyl, propyl, isopropyl, butyl and the like.

The polyimides of the present invention have high tensile properties,exceptional stability to heat and water and good electric properties.Thus, these polyimides are particularly useful as shaped structures suchas films, fibers, filaments and composites with reinforcing agents suchas glass fabrics, graphites and boron fibers.

The starting materials employed in the preparation of the polyimides ofthis invention are s-triazine compounds containing two primary aryl,alkyl and cycloalkyl amino groups and aromatic tetracarboxylic acidanhydrides. The triazine based diamines are characterized by theformula:

wherein R and R are as defined above. More specifically, R is I whereinX is sulfur, oxygen, sulfone, methylene or alkyl or aryl substitutedmethylene groups c. alkylene groups having from two to eight carbonatoms,

and d. cycloalkyl groups, such as cyclopentyl, cyclohexyl and the like.The blocking group R mentioned above can be hydrogen, phenyl or an aminogroup illustrated below:

-NH,, dialkyiamino groups such as, dimethylamino, diethylamino,dipropylamine, diisopropylamino, dibutylamino and the like, pyrrolidino,piperidino, anilino, N-(lower)alkyl anilino compounds such as N-methylanilino, N-ethyl anilino, N-butyl anilino, N-arylanilino compounds suchas diphenylamino, N-naphthyl anilino, phenyl, and the like.

The following s-triazine compounds exemplify a few types of diaminesthat can be employed in preparing the polyimides of this invention.

The s-tn'azine diamines discussed above generally have higher molecularweights than the diamines employed in preparing the prior artpolyimides. This imparts an important advantage to the s-triazine basedpolyimides over the prior art polyimides since the polyamic acids ofthis invention evolves,

on a weight basis, less water of condensation during the formation ofpolyimides. This water of condensation has a tendency to be entrapped inthe polyimide resins causing voids, which usually open during a hightemperature use providing additional surface for oxidative attack. Forthis reason it is desirable to keep the water of condensation to aminimum. In the 3 4 Prior an Plyimide5 the water of wfldensafion usuallyabom The following species are typical of tetracarboxylic acid di- 9 Pon a weigh basis- In the S'n'iaime Polyl'mides anhydrides suitable forpracticing the invention: stantially less water is evolved, generallyabout percent or 3,3,9,10-perylene tetracarboxylic dianhydride less.Thus the thick moldings and composites of low voidconl,4,5,8-naphthalene tetracarboxylic dianhydride tent are more rea ilypr par d by empl ying the -lli li 5 2,6-dichloronaphthalenel,4,5,8-tetracarboxylic dianpolyimides of this invention. h d id Thedianhydrides useful in this invention are characterized2,7-dichloronaphthalene-l ,4,5,8-tetracarboxylic dianby the generalformula: h drid 2,3 ,6,7-tetrachloronaphthalenel ,4,5,8-tetracarboxylicdi- 0 o 10 anhydride i ii phenanthrene- 1 ,8,9, IO-tetracarboxylicdianhydride 2,3,3,,4-benzophenone tetracarboxylic dianhydridePyromellitic dianhydride A g 1 3,3 ,4,4 -benzophenone tetracarboxylicdianhydride 2,2',3,3'-benzophenone tetracarboxylic dianhydride3,3',4,4'-diphenyl tetracarboxylic dianhydride wherein the tetravalentradical 2,2,3,3-diphenyl tetracarboxylic dianhydride 2,2-bis-( 3,4-dicarboxyphenyl )propane dianhydride 2,2-bis-bis(2,3-dicarboxyphenyl)propane dianhydride R bis-( 3,4-dicarboxyphenyl)ether dianhydride a a t X t a bis-( 3,4-dicarboxyphenyl)sulfonedianhydride 1 1-bis-( 2,3-dicarboxyphenyl )ether dianhydride l l-bis-(3,4-dicarboxyphenyl )ether dianhydri de is as heretofore defined and maybe selected from the followbis-(2,3-dicarboxyphenyl)methane dianhydrideing general groups: aromatic, aliphatic, cycloaliphatic, hererobi-.(3,4-di arboxy henyhmethane dianhydride cyclic, combinations ofaromatic and aliphatic, and sub- 2,3,6,7 ht h 1e tetracarboxylic dianhdride stituted groups thereof. The R groups may be characterized by1,2,4,5- h h 1 t b x li dianhydride the foll wing ruel,2,5,6-naphthalene tetracarboxylic dianhydride benzenel,2,3,4-tetracarboxylic dianhydride pyrazine-2,3,5,6-tetracarboxylicdianhydride thiophene-2,3,4,5-tetracarboxylic dianhydride, anddianhydrides having the general structure:

i it wherein R is selected from the group consisting of 0--, Whfi'e l a2', R3 and 4 are each members Selected from hydrogen, alkyl, aryl, andaralkyl.

The polyimides are prepared by a process comprising reacting the abovedescribed s-triazine diamines with dianhydrides 0 R 0 0 in an organicreaction medium which is a solvent for at least ll l g 8 one of thereactants, preferably under substantially anhydrous s, -s0,, N, 0- a R4R4 R4 R4 conditions, at a temperature below 100 C. The product of this IA l reaction is a polyamic acid represented by the following s -0 1-0,P-, and general formula: A Bi 3 -a wherein R and R are alkyl or aryl,and substituted groups N O in these dianhydrides every carbonyl group isattached directly to a separate carbon atom of the aromatic radical, thecarbonyl groups being ortho or peri to each other so that the five orsix membered anhydride rings are formed respectively.

The preferred aromatic dianhydrides are those in which the carbon atomsof each pair of carbonyl groups are directly at- M sPedficany thereaction f q O tached to ortho carbon atoms in the R group to provide afivey a number of y The s-mazme dlamme and the membered ring as follows:dianhydride can be premixed as dry solids in equimolar amounts and theresulting mixture can be added, in small portions and with agitation, tothe organic solvent. This method is O E E E g particularly effective inreactions which are relatively exotherm mic. However, it is alsopossible to add slowly with agitation al; i3=':- the solvent to thepremixed reactants. Another variation is to I U I dissolve thes-triazine diamine in the solvent and then add thereto the dianhydrideat a rate that provided a controllable rate of reaction. It is alsopossible to add the reactants separately and in small portions to thesolvent or to dissolve the reactants in separate portions of the solventand then slowly adding the two solutions to the reaction vessel.

The degree of polymerization of the polyamide acid is subject todeliberate control. The use of equal molar amounts of the reactantsunder the prescribed conditions provides polyamide acids of very highmolecular weight. The use of either reactant in large excess limits theextent of polymerization. However, the scope of the process encompassesthe use of up to 5 percent excess of either the diamine or thedianhydride. More than 5 percent excess of either reactant results in anundesirably low moleculer weight polyamic acid. For some purposes, it isdesirable to use l-3 percent excess of either reactant, preferably thedianhydride. Besides using an excess of one reactant to limit themolecular weight of the polyamic acid, a chain tenninating agent such asphthalic anhydride or aniline may be used to "cap" the ends of thepolymer chains.

In the preparation of the polyamic acid intermediate, it is essentialthat the molecular weight be such that the inherent viscosity of thepolyamic acid is at least 0.], preferably 0.3-5.0. The inherentviscosity is measured at 30 C. at a concentration of 0.5 percent byweight of the polymer is a suitable solvent, e.g.,N,N-dimethylacetamide, N-methyl pyrrolidone, dimethyl formamide, etc. Tocalculate inherent viscosity, the viscosity of the polymer solution ismeasured relative to that of the solvent alone.

Inherent viscosity= Natural logarithm X wherein C is the concentrationexpressed in grams of polymer per 100 milliliters of solution. As knownin the polymer art inherent viscosity is directly related to themolecular weight of the polymer.

The quantity of organic solvent used in the preferred process need onlybe sufficient to dissolve enough of one reactant, preferably thediamine, to initiate the reaction of the diamine and the dianhydride.For forming the composition into shaped articles, it has been found thatthe most successful results are obtained when the solvent represents atleast 60 percent of the polymeric solution. That is, the solution shouldcontain 0.05-40 percent of the polymeric component. The viscous solutionof the polymeric composition containing to 40 percent polyamic acid inthe polymeric component dissolved in the solvent may be used as such forforming shaped structures.

The shaped articles containing the polyarnic acid are then converted tothe respective polyimide shaped articles. It should be understood thatthe conversion process to be described also apply to compositionscontaining salt derivatives of polyamic acids, e.g., the ammonium ortriethyl ammonium salt of the polyarnic acids, instead of the polyarnicacids themselves.

The solvents useful in the solution polymerization process forsynthesizing the intermediate polyamic acid compositions in the processof preparing the polyimides are the organic solvents whose functionalgroups do not react with either of the reactants (the diamines or thedianhydrides) to a greater extent than the reactants, preferably forboth of the reactants. The normally liquid organic solvents of theN,N-dialkylcarboxylamide class are useful as solvents in the process ofthis invention. The preferred solvents are the lower molecular weightmembers of this class, particularly N,N-dimethylformamide andN,N-dirnethylacetamide. They may easily be removed from thepolyamide-acid and/or polyarnide acid shaped articles by evaporation,displacement or diffusion. Other typical compounds of this useful classof solvents are:

N,N-diethylformamide N,N-diethylacetamide N,N-dimethylmethoxy acetamideN-methyl caprolactam, etc.

Other solvents which may be used in the present invention are:

dimethylsulfoxide N-methyl-2-pyrrolidone tetramethyl urea pyridinedimethylsulfone hexamethylphosphoramide tetramethylene sulfone formamideN-methylformamide butyrolactone.

The solvents can be used alone, in combinations of solvents, or incombination with poor solvents such as benzene, benzonitrile, dioxane,xylene, toluene and cyclohexane.

To determine a specific time and a specific temperature for forming thepolyamide acid of one of the specified diamines and a specifieddianhydride, several factors must be considered. The maximum permissibletemperature will depend on which of the two diamines is used, thedianhydride used, the particular solvent, the percentage of polyarnicacid desired in the final composition and the minimum period of timethat one desired for the reaction. For most combinations ofmetaphenylenediamine or para-phenylenediamine s-triazine derivatives andthe dianhydrides falling within the definitions given above, it ispossible to form compositions of percent polyamic acid by conduction thereaction below 100 C. However, temperatures up to C. may be tolerated toprovide shapeable compositions. However, to obtain the maximum inherentviscosity, i.e., maximum degree of polymerization, for any particularcombination of s-triazine diamine, dianhydride, solvent, etc., and thusproduce shaped articles such as films and filaments of optimumtoughness, it has been found that the temperature throughout thereaction should be maintained below 60 C., preferably below 50 C.

The polyamic acid prepared as described above can be isolated byevaporating the solvent at temperatures lower than 70 C. The polyamicacid is soluble in organic solvents and in ammonium hydroxide to give awater soluble solution. Accordingly, the polyimides of this inventioncan be obtained both from an organic or from an aqueous medium. Theavailability of both of these mediums from which triazine basedpolyimides can be obtained represents a very important advantage forobtaining high temperature polyimide films and coatings.

The polyamic acid may be converted to polyimide by a varity of methods.One method comprises converting the polyamic acid by heating it above 50C. Heating serves to convert pairs of amide and carboxylic acid groupsto imide groups. Heating may be conducted for a period of a few secondsto several hours. It has been found that after the polyamide acid hasbeen converted to the polyimide in accordance with the above describedheat conversion, if the polyimide is further heated to a temperature of300-500 C. for a short period, improvements in the thermal andhydrolytic stabilities of the polyimide are obtained.

A second method for converting the polyamic acid composition to thepolyimide thereof is a chemical treatment and involves treating thepolyamic acid composition with a dehydrating agent alone or incombination with a tertiary amine, e.g., acetic anhydride or an aceticanhydride-pyridine mixture. The polyamic acid shaped article can betreated in a bath containing acetic anhydride-pyridine mixture. Theratio of acetic anhydride to pyridine may vary from just above zero toinfinite mixtures. It is believed that the pyridine functions as acatalyst for the action of the cyclizing agent, the acetic anhydride.Other possible dehydrating agents for use include propionic anhydride,butyric anhydride, valeric anhydride and mixed lower fatty-acidanhydrides. Other tertiary amine catalysts include triethylamine,isoquinoline, 01,13 or gamma picoline, 2,5-lutidine, etc.

A third method for conversion involves treatment with a carbodiirnide,e.g., dicylohyxylcarbodiimide. The carbodiimide also serves to dehydratethe polyamic-acid and to act as an eflective cyclyzing agent.

As a fourth method of conversion, a combination treatment may be used.The polyamic acid may be partially converted to the polyimide in achemical conversion treatment and then cyclization to the polyimide maybe completed by subsequent heat treatment. The conversion of thepolyamic acid to the polyimide in the first step should not exceed 50percent if it is desired to shape the composition into suitable forms.After shaping, the completion of the cyclization of thepolyimide/polyamic acid may be accomplished.

it should be understood that instead of shaping the polyamic acidcomposition into the usual articles, the polyamic acid composition inthe solvent may be used as a liquid coating composition. Such coatingcompositions may be pigmented with such compounds as titanium dioxide inamounts of -200 percent by weight. These coating compositions may beapplied to a variety of substrates, for example, metals, e.g., copper,brass, aluminum, steel, etc., the metals in the form of sheets, fibers,wires, screening, etc; glass in the form of sheets fibers, foams,fabrics, etc.; polymeric materials, e.g., cellulosic materials such ascellophane, wood, paper etc., polyolefins such as polyethylene,polypropylene, polystyrene, etc., perfluorocarbon polymers such as,polytetrafluoroethylene, copolymer of tetrafluoroethylene withhexafluoropropylene, etc., polyurethanes, all polymeric materials in theform of sheets, fibers, foams, woven and non-woven fabrics, screening,etc.; leather sheets; etc. The polyamic acid coatings are then convertedto polyimide coatings by one or more of the processes to be described.

The polyimides of this invention find many applications in a widevariety of physical shapes and forms. Among the most significant ofthese forms are films and fibers. The useful combination of thedesirable physical and chemical characteristics of this polymer isunique. Films and fibers of this polymer not only possess excellentphysical properties at room temperature, but retain their strength andexcellent response to workloading at elevated temperatures for prolongedperiods of time. Behavior of this type offers commercial utility in awide range of end uses. These polyimide polymers display excellentresistance to strong acids and alkalies, to corrosive atmospheres,outstanding resistance to degradation by high energy particles and gammaray radiation. The polymer resists melting upon exposure at 500 C. forextended periods while retaining hitherto unrealized high proportions ofroom temperature physical properties. Because of the unusual andsurprising solubility of the polymer precursor in the process ofpreparation, this polymer precursor may be processed into shapedarticles such as films and fibers by conventional techniques and thenconverted in situ to the polyimide polymer. Solutions of the s-triazinecontaining polyamic acids can be used to impregnate reinforcing fibersand fabrics like glass, boron, metal oxide whiskers and graphite. Theseprepregs can then be cured to form rigid polyimide laminates orcomposites or to form strong thermally resistant structural adhesivebonds between aluminum, stainless steel, titanium or other metals.

Films formed from the polymer of this invention may be used whereverfilms have heretofore been used. They serve advantageously in anextensive variety of wrapping, packaging and bundling applications.Additionally, the polymer and filmforming polymer may be used inautomobile and aviation interior head lining materials, decorative trim,high temperature electrical insulation such as for slot liners, in drytransformers, capacitors, cable wrappings, etc., packaging of items tobe exposed to high temperature or high energy radiation while within thepackage, corrosion-resistant pipe, duct work, containers and containerlinings, and laminating structures where the films are bonded to thesheet metal or foils, and a variety of other similar and related uses.in fiber form, the polymer offers possibilities for high temperatureelectrical insulation,

protective clothing and curtains, filtration media, packing andgusseting materials, brake linings and clutch facings.

The particular advantage of the triazine-based polyimides of thisinvention is that the polyamic acid is soluble in ammonium hydroxide togive aqueous solutions. This advancement is of great importance for anumber of reasons. First of all, by employing the polyimides of thisinvention it is possible to form the desired films, fibers or otherarticles from the aqueous solutions and thus avoid the undesirable airpollution problems which are ever present when organic solvents areemployed. This also provides an economic advantage since the organicsolvents are more expensive than water.

The polyimides of this invention have a high nitrogen content from thes-triazine ring and therefore are also useful as ablative heat-shieldmaterials. This stems from the fact that chars containing interstitialnitrogen atoms have lower thermal conductivity than graphite or carbon.

Furthermore, the insertion of the s-triam'ne ring into the polyimidechains increases the glass transition, Tg. of the polymer. This makes itpossible for the s-triazine polyimides to be used at higher temperaturesthan the prior art polyimides. Since at temperatures above thetransition temperature the polymers lose their stiffness and mechanicalproperties, any increase in transition temperature is of greatimportance. The presence of s-triazine in the polyimide chains alsogives the resin greater stiffness than is obtainable with the knownpolyimides. The improvement of this property is important sincestiffness at high temperatures is required in laminates and compositesused in structural parts such as in supersonic aircraft.

To further illustrate the nature of this invention and the processemployed in preparing the triazine-based polyimides, the followingexamples are presented below.

EXAMPLE 1 To a 300 ml flask equipped with a stirrer and CaCl tube, 8.4lg., (0.025 moles) of 2-dimethylamino-4,6-bis(maminoanilino)-s-triazinedissolved in 94 ml of dry dimethyl acetamide was added. Benzophenonetetracarboxylic dianhydride (BTDA), 8.06 g (0.025 moles) was slowlyadded to the stirred solution. A mild exotherm to 35 C. was noted and aviscous solution was produced.

A 10 mil film from the solution was cast on aluminum foil and placed inan air circulation oven at 25 C. The oven was heated to 300 C. in 45minutes. The coated foil was then removed from the oven and placed in ahydrochloric acid solution to dissolve the aluminum. The polyimide filmwas washed with water and dried.

The polyimide film was repeatedly flexed and creased without breaking.it charred but did not burn in a flame. A thermal gravimetric analysis(TGA) in air showed good thermal stability without weight loss up to 425C. The film had an initial tensile strength of 14,450 psi. and modulusof 363,000 psi. After 1 week of aging at 300 C. in air the tensilestrength was 16,230 psi and modulus 492,000 psi.

EXAMPLE 2 i A 300 ml reaction vessel equipped as in Example I, wascharged with 8.41 g (0.025 moles) of 2-dimethylamino-4,6- bis(m-aminoanilino)-s-triazine and ml of dry dimethyl acetamide. Solidpyromellitic dianhydride 5.45 g (0.025 moles) was added slowly to thisstirred solution as the reaction temperature increased, but was notallowed to exceed 35 C. After solution was complete the reaction mixturewas concentrated under vacuum at a temperature not exceeding 30 C.Approximately half of the dirnethyl acetamide was evaporated so that aviscous syrup suitable for casting was obtained.

A 10 mil film was cast from the solution on aluminum foil and placed inan air circulation oven at 25 C. The oven was heated to 300 C. in 45minutes to cure the film. The foil was dissolved in hydrochloric acidand the polymer film washed with water and dried.

The film was amber colored, tough, flexible and nonflammable.

EXAMPLE 3 To a 200 ml. flask equipped as in Example 1, was added 6.70 g(0.020 moles) of 2-dimethylamino-4,6-bis(maminoanilino)-s-triazinedissolved in 70 ml of anhydrous dimethyl acetamide. Solid benzophenonetetracarboxylic dianhydride, 6.42 g., (0.020 moles), was slowly added tothe stirred solution. The solution became more viscous and thetemperature increased to 33 C.

The clear dimethylacetamide solution was added dropwise over a 45 minuteperiod to a 2 liter flask containing ml concentrated ammonium hydroxidedissolved in 1,500 ml of isopropanol. During the addition the mixturewas agitated with a Lighting Mixer." The precipitated ammonium salt ofthe polyamic acid was filtered off and washed with isopropanol anddiethyl ether. This salt was dried at 45 C. under vacuum.

The polyamic acid salt was dissolved in water to yield a percentsolution. Films were cast and cured directly to yield a polyimidecoating on a metal sheet. Films of better clarity and physicalproperties were obtained if 1 to 15 percent by volume of dimethylforrnamide was added to the aqueous solution.

EXAMPLE 4 To a 200 ml flask equippred as in Example 1, was charged 2.3g. (0.005 moles) of 2-diphenylamino4,6-bis(maminoanilino)-s-triazinedissolved in 40 ml of N-methyl pyrrolidone. Solid benzophenonetetracarboxylic dianhydride, 1.53 g. (0.005 moles), was slowly added tothe stirred solution. The solution became more viscous and thetemperature increased to 30 C.

This polyamic acid had an inherent viscosity of 0.72. The ammoniatedpolyamic acid from this run required a 50/50 mixture of water anddimethyl acetamide to form a homogeneous solution.

A film was cast of the polyamic acid from N-methyl pyrrolidone solutionand cured at 300 C. for 1 hour. This film was isothermally aged in airat 300 C. After 500 hours the film was still flexible and retained 96percent of its original weight.

EXAMPLE 5 To a 200 ml flask equipeed as in Example 2, was charged 4.6 g.(0.01 moles) of 2-diphenylamino-4,6-bis(maminoanilino)-s-triazinedissolved in 50 ml of anhydrous dimethyl acetamide. To the stirredsolution were added 2.27 g. (0.0104 moles) of solid pyromelliticdianhydride while the reaction temperature was maintained below 30 C.

A film was cast of the polyamic acid from the dimethyl acetamidesolution and cured at 300 C. for 1 hour. This film was isothermally agedin air at 300 C. for 666 hours and was found to be still flexible andtough having retained 94 percent of its original weight.

EXAMPLE 6 2-Diphenylamino-4,6-bis(4,4-aminooxydianilino)-striazine wasreacted with a stoichiometric equivalent of pyromellitic dianhydride indimethylacetamide by the procedure described in Example 5. The curedpolyimide film which was initially flexible becamse embrittled after 240hours of isothermal aging at 300 C. in air.

EXAMPLE 7 2-Phenyl-4,6-bis(m-aminoanilino)-s-triazine was reacted with astoichiometric equivalent of benzophenone tetracarboxylic dianhydride bythe procedure described above in Example 5. The cured polyimide film wasflexible and after 1,300 hours of isothermal aging in air at 300 C.retained 92.4 percent of its original weight.

The polyamic acid from the room temperature reaction of2-phenyl-4,6-bis( m-aminoanilino )-s-t-n'azine and benzophenonetetracarboxylic dianhydride of inherent viscosity 1.1 was precipitatedand the ammonium salt in water prepared. Films cast from water and curedat 300 C. retained 91 percent of their initial weight after isothermalaging for 500 hours in air at 300 C.

EXAMPLE 8 2-Amino-4,6-bis(m-aminoanilino)-s-triazine was reacted with astoichiometric equivalent of pyromellitic dianhydride by theproceduredescribed above in Example 5. The polyamic acid of inherent viscosity0.89 was cast as a film on polyethylene and the dried film was removedfrom the polyethylene and cured at 300 C. for 1 hour. The cured film didnot show loss in weight before 450 C. when a thermogravimetric analysiswas run in air at a heating rate of 20 C. per minute. Upon isothermalaging in air at 300 C. the film retained 86 percent of its originalweight for 330 hours.

EXAMPLE 9 In a 1 liter three-necked flask equipped with a nitrogen purgestirrer and thermometer was charged 109.7 g. of 2-diphenylamino-bis(4,-m-aminoanilino)-s-triazine dissolved in anhydrousdimethyl acetamide. The solution was cooled to 1015 C. and 64.4 g. ofbenzophenone tetracarboxylic dianhydride was added in three equalportions at a rate so that the reaction temperature did not go above 20C. After 45 minutes of stirring a 20 percent solids polyamic acidsolution was produced. The intrinsic viscosity of the polyamic acid was0.51.

This solution was used to impregnate 181 E glass fabric (A1 amino silanefinish). The fabric was twice passed through the solution and thenthrough coater rolls with a 16 mil gap. The impregnated fabric washeated at 150 C. for 1 minute to reduce the solvent content to 12percent and then cut into 5 X 5" squares for laminating. An 18 plylaminate was prepared (five impregnated plys for one dry ply of 181 E)by heating in a press at 750 psi at 500 C. for one-half hour followed byone-half hour at 600 great rigidity and excellent color was produced.

EXAMPLE 1O 2-N-methylanilino-bis(4,6-ortho aminoanilino)-s-triazine(0.03 moles) 10.1 g. and benzophenone tetracarboxylic dianhydride (0.03moles) 9.66 g. is reacted together at room temperature with stirring in96 ml of anhydrous DMAC. When a film of the resulting polyamic is castand heated to 300 C. a stiff, yellow polyimide film is produced.

EXAMPLE 1 l 2-Amino-bis(4,6paraaminoanilino)-s-triazine (0.03 moles)9.25 g. and pyrazine tetracarboxylic dianhydride (0.03 moles) 6.6 g. isreacted together at room temperature with stirring in 70 ml of anhydrousdimethyl acetamide. The dimethyl acetamide is removed by heating thesolution under vacuum and the precipitated solid is isolated and heatedto 300 C. under nitrogen to fully convert it into the correspondingpolyimide. When this polyimide is heated in air to 500 C. the weightloss is very slight.

EXAMPLE 12 2-Anilino-bis(4,6 paraaminoanilino)-s-triazine (0.3 moles), 115 g. and l,4,5,8-naphthalentetracarboxylic dianhydride (0.3 moles) 80.5g. are reacted together at room temperature, with stirring in 900 ml ofanhydrous N-methyl pyrrolidone. This solution is used to impregnate 181E glass fabric cloth containing a 1100 finish (amino silane) by passingthe cloth twice through the polyamic acid solution. The saturated glassfabric cloth is heated for 75 minutes at C. in an air oven to B-stagethe resin. The resulting prepreg is cut into 5 X 5 C. a light coloredlaminate of i inch sheets and an 18 ply laminate prepared by using a dryply of glass fabric for every five plys of prepreg. lnitial contact inthe press for l E minutes at p s i and 600 F. is used followed by a curecycle of 30 minutes at 600 F. and 250 p s i The laminate containspercent resin and a very low void content as measured by specificgravity.

EXAMPLE l3 2-Diphenylamino-bis(4,6-meta amino anilino)-s-triazine andbenzophenone tetracarboxylic acid dianhydride are reacted together atroom temperature with stirring in anhydrous dimethyl acetamide yieldingthe corresponding polyamic acid.

EXAMPLE l4 2-Piperidino bis(4,6-beta aminoethyl amino)-s-triazine (0.03moles) 8.4 g. and pyromelletic dianhydn'de (0.03 moles) 6.54 g. werereacted together at room temperature in 90 ml of dimethyl formamide. Theresulting polyamic acid had an inherent viscosity of 0.95. A film of thepolyamic acid Wm cast and cured at 300 C. for 10 minutes. The cured filmwas transparent and appeared flexible and tough after repeated creasing.

What is claimed is:

1. A polyimide consisting essentially of the recurring unit wherein X issulfur, oxygen, sulfone, methylene or alkyl or aryl substitutedmethylene groups c. alkylene groups having from two to eight carbonatoms,

and

d. cycloalkyl groups,

R is hydrogen, amino, diarylamino, di(lower)alkyl amino,

anilino, N-(lower)alkyl anilino, diphenylamino, pyrrolidino, piperidinophenyl or chloro groups;

n is an integer of 5 or more. said polyimide having been prepared fromthe corresponding polyamic acid having the inherent viscosity of atleast 0.1, measured at C. at a concentration of 0.5 percent by weight ofthe polymer in a solvent selected from N,N-dimethylacedamide, N- methylpyrrolidone or dimethyl formamide.

2. A polyimide according to claim 1 wherein said R group has thestructure selected from ii- @l 3. A polyimide according to claim 1wherein said R is a phenylene.

4. A polyimide according to claim 1 wherein R radical.

5. A polyimide according to claim 1, the recurring unit is an amine saidpolyimide having 6. A polyimide according to claim 1, said polyimidehaving ll A 7. A polyamic acid consisting essentially of the recurringunit wherein RR and n are as defined in claim 1, said polyamic acidhaving the inherent viscosity of at least 0.] measured at 30 C at aconcentration of 0.5 percent by weight of the polymer in a solventselected from N,N-dimethylacetamide, N-methyl pyrrolidone or dimethylformamide.

l t IIK

2. A polyimide according to claim 1 wherein said R group has thestructure selected from
 3. A polyimide according to claim 1 wherein saidR'' is a phenylene.
 4. A polyimide according to claim 1 wherein R2 is anamine radical.
 5. A polyimide according to claim 1, said polyimidehaving the recurring unit
 6. A polyimide according to claim 1, saidpolyimide having the recurring unit
 7. A shapeable compositioncomprising a linear film-forming polyimide consisting essentially ofrecurring units of
 8. A composition of claim 7 wherein said polyimidehas the recurring unit selected from
 9. A polyamic acid consistingessentially of the recurring unit